There are very bad motion artifacts associated with current three-dimensional (3-D) projectors that are caused by a phase difference between the projected images presented to the left and right eyes, respectively. Moving objects may appear at the wrong depths, depending on the direction the respective moving objects are moving. Even worse, if the moving objects happen to be moving vertically, there may be a visually disconcerting “twisting” caused by the projected images presented to the left and right eyes, respectively. The left and right eyes may not even be able to converge on the respective vertically moving object. There may also be a z-direction pulsing introduced for 24 Hz source material because of the combined effect of the phase difference and the retrograde motion caused by showing each frame twice.
As shown, for example, in FIG. 1A, with two projectors, the left (L) and right (R) images for the left and right eyes, respectively, may be shown on the screen at the same time, as indicated at 110, so there is no relative delay, corresponding to a phase difference of 0 degrees (PD=0, as shown at 125). As shown, for example, in FIG. 1A, the field time is the same as the frame time. However, there is a significant additional cost associated with using an extra projector, as well as the added complexity of increased optical alignment, and the like.
As shown, for example, in FIG. 1B, with only one projector, the left (L) image 120 and right (R) image 130 may be shown on the screen sequentially. If one image, such as the left (L) image 120 (as shown in FIG. 1B), is shown on the screen first and then the other image, such as the right (R) image 130 (as shown in FIG. 1B), is shown on the screen second, there is a maximal relative delay, corresponding to a phase difference of 180 degrees (PD=180, as shown at 125). As shown, for example, in FIG. 1B, the field time is one half of the frame time.
As shown, for example, in FIG. 1C, for 24 Hz source material, each of the left (L) and right (R) images 120, 130 is shown twice, corresponding to a phase difference of 90 degrees (PD =90, as shown at 125). In this case, the field time is one quarter of the frame time.
As shown, for example, in FIG. 1D, with very fast polarized switching devices, each of the images 120, 130 could be shown three or more times (four times in FIG. 1D), corresponding to a phase difference of 60 degrees or less (45 degrees in FIG. 1D, PD =45, as shown at 125), depending on the number of times per frame each of the left (L) and right (R) images 120, 130 is shown. In these cases, the field times would be one sixth or less of the frame times. Generally, with sufficiently fast polarized switching devices, each of the left (L) and right (R) images 120, 130 could be shown n times, corresponding to a phase difference of 180/n degrees (PD =180/n), where n is the number of times per frame each of the left (L) and right (R) images 120, 130 is shown. In this case, the field time would be (1/[2n])-th of the frame time. However, there is a significant extra cost associated with switching faster in terms of bandwidth, brightness, the higher cost of the faster switching device, and the like.
If an object is moving at a speed of K pixels per frame, this causes a relative shift of (Δφ/360°)×K pixels in the direction of motion, where Δφ is the phase difference (PD) 125. In other words, one eye will see the object displaced by (Δφ/360°)×K pixels in the direction of motion, relative to where that eye should see the object. For example, as shown in FIGS. 9A-9D, the object (a man looking through a camera on a tripod) shown therein is moving to the right at 12 pixels per frame. A phase difference Δφ=90° may cause a relative shift of about (Δφ/360°)×K=(90°/360°)×12=3, so that one eye will see the man looking through the camera on the tripod displaced by about 3 pixels in the direction of motion, relative to where that eye should see the man looking through the camera on the tripod.
Side-to-side motion of near-field objects may cause the near-field objects (such as things in the foreground) to appear closer or farther than the near-field objects should appear. This may not usually be a big problem. However, for a far-field object (such as the distant background as the camera pans across a scene), movement to one side may cause the far-field object to appear nearer, but movement in the opposite direction may cause the far-field object to appear “farther than infinity.” In other words, the left and the right eyes may have to point away from each other, which is not normal and may be very disorienting or even painful for the viewer.
For any object moving up or down vertically (or, indeed, any direction other than perfectly horizontally), one eye must look at a point either higher or lower than the other eye. Again, this is not normal and may be disconcerting and very undesirable. The various types of stereoscopic phase-lag distortion under motion in a 3-dimensional video display described above may be proportional to the phase difference between the projected images presented to the left and right eyes, respectively.